In "The Merry Men"

Charles pays a visit to his Uncle Gordon and cousin Mary Ellen. They live on the island of Eilean Aros, which has dangerous waters and has been the site of many shipwrecks.

Indeed, the island is surrounded by treacherous reefs, known locally as "the Merry Men". They are so named because "the noise of them seemed almost mirthful [. ..] yet instinct with a portentous joviality. Nay, and it seemed even human".